updating PHP

Hello,

I am running Moodle on Windows Server 2008 with IIS 7.  I am on Moodle 2.6 and need to update my version of PHP from 5.3.21 to 5.5.5 however every time I change it in IIS through php manager, I can no longer access my Moodle site.  How do I go about making this change so Moodle also works?  Thank you in advance.